Merge branch 'slab/for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/penber...

[mirror_ubuntu-artful-kernel.git] / arch / powerpc / kernel / entry_64.S

/*
 *  PowerPC version 
 *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
 *  Rewritten by Cort Dougan (cort@cs.nmt.edu) for PReP
 *    Copyright (C) 1996 Cort Dougan <cort@cs.nmt.edu>
 *  Adapted for Power Macintosh by Paul Mackerras.
 *  Low-level exception handlers and MMU support
 *  rewritten by Paul Mackerras.
 *    Copyright (C) 1996 Paul Mackerras.
 *  MPC8xx modifications Copyright (C) 1997 Dan Malek (dmalek@jlc.net).
 *
 *  This file contains the system call entry code, context switch
 *  code, and exception/interrupt return code for PowerPC.
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 */

#include <linux/errno.h>
#include <asm/unistd.h>
#include <asm/processor.h>
#include <asm/page.h>
#include <asm/mmu.h>
#include <asm/thread_info.h>
#include <asm/ppc_asm.h>
#include <asm/asm-offsets.h>
#include <asm/cputable.h>
#include <asm/firmware.h>
#include <asm/bug.h>
#include <asm/ptrace.h>
#include <asm/irqflags.h>
#include <asm/ftrace.h>
#include <asm/hw_irq.h>
#include <asm/context_tracking.h>

/*
 * System calls.
 */
        .section        ".toc","aw"
.SYS_CALL_TABLE:
        .tc .sys_call_table[TC],.sys_call_table

/* This value is used to mark exception frames on the stack. */
exception_marker:
        .tc     ID_EXC_MARKER[TC],STACK_FRAME_REGS_MARKER

        .section        ".text"
        .align 7

#undef SHOW_SYSCALLS

        .globl system_call_common
system_call_common:
        andi.   r10,r12,MSR_PR
        mr      r10,r1
        addi    r1,r1,-INT_FRAME_SIZE
        beq-    1f
        ld      r1,PACAKSAVE(r13)
1:      std     r10,0(r1)
        std     r11,_NIP(r1)
        std     r12,_MSR(r1)
        std     r0,GPR0(r1)
        std     r10,GPR1(r1)
        beq     2f                      /* if from kernel mode */
        ACCOUNT_CPU_USER_ENTRY(r10, r11)
2:      std     r2,GPR2(r1)
        std     r3,GPR3(r1)
        mfcr    r2
        std     r4,GPR4(r1)
        std     r5,GPR5(r1)
        std     r6,GPR6(r1)
        std     r7,GPR7(r1)
        std     r8,GPR8(r1)
        li      r11,0
        std     r11,GPR9(r1)
        std     r11,GPR10(r1)
        std     r11,GPR11(r1)
        std     r11,GPR12(r1)
        std     r11,_XER(r1)
        std     r11,_CTR(r1)
        std     r9,GPR13(r1)
        mflr    r10
        /*
         * This clears CR0.SO (bit 28), which is the error indication on
         * return from this system call.
         */
        rldimi  r2,r11,28,(63-28)
        li      r11,0xc01
        std     r10,_LINK(r1)
        std     r11,_TRAP(r1)
        std     r3,ORIG_GPR3(r1)
        std     r2,_CCR(r1)
        ld      r2,PACATOC(r13)
        addi    r9,r1,STACK_FRAME_OVERHEAD
        ld      r11,exception_marker@toc(r2)
        std     r11,-16(r9)             /* "regshere" marker */
#if defined(CONFIG_VIRT_CPU_ACCOUNTING_NATIVE) && defined(CONFIG_PPC_SPLPAR)
BEGIN_FW_FTR_SECTION
        beq     33f
        /* if from user, see if there are any DTL entries to process */
        ld      r10,PACALPPACAPTR(r13)  /* get ptr to VPA */
        ld      r11,PACA_DTL_RIDX(r13)  /* get log read index */
        ld      r10,LPPACA_DTLIDX(r10)  /* get log write index */
        cmpd    cr1,r11,r10
        beq+    cr1,33f
        bl      .accumulate_stolen_time
        REST_GPR(0,r1)
        REST_4GPRS(3,r1)
        REST_2GPRS(7,r1)
        addi    r9,r1,STACK_FRAME_OVERHEAD
33:
END_FW_FTR_SECTION_IFSET(FW_FEATURE_SPLPAR)
#endif /* CONFIG_VIRT_CPU_ACCOUNTING_NATIVE && CONFIG_PPC_SPLPAR */

        /*
         * A syscall should always be called with interrupts enabled
         * so we just unconditionally hard-enable here. When some kind
         * of irq tracing is used, we additionally check that condition
         * is correct
         */
#if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_BUG)
        lbz     r10,PACASOFTIRQEN(r13)
        xori    r10,r10,1
1:      tdnei   r10,0
        EMIT_BUG_ENTRY 1b,__FILE__,__LINE__,BUGFLAG_WARNING
#endif

#ifdef CONFIG_PPC_BOOK3E
        wrteei  1
#else
        ld      r11,PACAKMSR(r13)
        ori     r11,r11,MSR_EE
        mtmsrd  r11,1
#endif /* CONFIG_PPC_BOOK3E */

        /* We do need to set SOFTE in the stack frame or the return
         * from interrupt will be painful
         */
        li      r10,1
        std     r10,SOFTE(r1)

#ifdef SHOW_SYSCALLS
        bl      .do_show_syscall
        REST_GPR(0,r1)
        REST_4GPRS(3,r1)
        REST_2GPRS(7,r1)
        addi    r9,r1,STACK_FRAME_OVERHEAD
#endif
        CURRENT_THREAD_INFO(r11, r1)
        ld      r10,TI_FLAGS(r11)
        andi.   r11,r10,_TIF_SYSCALL_T_OR_A
        bne     syscall_dotrace
.Lsyscall_dotrace_cont:
        cmpldi  0,r0,NR_syscalls
        bge-    syscall_enosys

system_call:                    /* label this so stack traces look sane */
/*
 * Need to vector to 32 Bit or default sys_call_table here,
 * based on caller's run-mode / personality.
 */
        ld      r11,.SYS_CALL_TABLE@toc(2)
        andi.   r10,r10,_TIF_32BIT
        beq     15f
        addi    r11,r11,8       /* use 32-bit syscall entries */
        clrldi  r3,r3,32
        clrldi  r4,r4,32
        clrldi  r5,r5,32
        clrldi  r6,r6,32
        clrldi  r7,r7,32
        clrldi  r8,r8,32
15:
        slwi    r0,r0,4
        ldx     r10,r11,r0      /* Fetch system call handler [ptr] */
        mtctr   r10
        bctrl                   /* Call handler */

syscall_exit:
        std     r3,RESULT(r1)
#ifdef SHOW_SYSCALLS
        bl      .do_show_syscall_exit
        ld      r3,RESULT(r1)
#endif
        CURRENT_THREAD_INFO(r12, r1)

        ld      r8,_MSR(r1)
#ifdef CONFIG_PPC_BOOK3S
        /* No MSR:RI on BookE */
        andi.   r10,r8,MSR_RI
        beq-    unrecov_restore
#endif
        /*
         * Disable interrupts so current_thread_info()->flags can't change,
         * and so that we don't get interrupted after loading SRR0/1.
         */
#ifdef CONFIG_PPC_BOOK3E
        wrteei  0
#else
        ld      r10,PACAKMSR(r13)
        /*
         * For performance reasons we clear RI the same time that we
         * clear EE. We only need to clear RI just before we restore r13
         * below, but batching it with EE saves us one expensive mtmsrd call.
         * We have to be careful to restore RI if we branch anywhere from
         * here (eg syscall_exit_work).
         */
        li      r9,MSR_RI
        andc    r11,r10,r9
        mtmsrd  r11,1
#endif /* CONFIG_PPC_BOOK3E */

        ld      r9,TI_FLAGS(r12)
        li      r11,-_LAST_ERRNO
        andi.   r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
        bne-    syscall_exit_work
        cmpld   r3,r11
        ld      r5,_CCR(r1)
        bge-    syscall_error
.Lsyscall_error_cont:
        ld      r7,_NIP(r1)
BEGIN_FTR_SECTION
        stdcx.  r0,0,r1                 /* to clear the reservation */
END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
        andi.   r6,r8,MSR_PR
        ld      r4,_LINK(r1)

        beq-    1f
        ACCOUNT_CPU_USER_EXIT(r11, r12)
        HMT_MEDIUM_LOW_HAS_PPR
        ld      r13,GPR13(r1)   /* only restore r13 if returning to usermode */
1:      ld      r2,GPR2(r1)
        ld      r1,GPR1(r1)
        mtlr    r4
        mtcr    r5
        mtspr   SPRN_SRR0,r7
        mtspr   SPRN_SRR1,r8
        RFI
        b       .       /* prevent speculative execution */

syscall_error:  
        oris    r5,r5,0x1000    /* Set SO bit in CR */
        neg     r3,r3
        std     r5,_CCR(r1)
        b       .Lsyscall_error_cont
        
/* Traced system call support */
syscall_dotrace:
        bl      .save_nvgprs
        addi    r3,r1,STACK_FRAME_OVERHEAD
        bl      .do_syscall_trace_enter
        /*
         * Restore argument registers possibly just changed.
         * We use the return value of do_syscall_trace_enter
         * for the call number to look up in the table (r0).
         */
        mr      r0,r3
        ld      r3,GPR3(r1)
        ld      r4,GPR4(r1)
        ld      r5,GPR5(r1)
        ld      r6,GPR6(r1)
        ld      r7,GPR7(r1)
        ld      r8,GPR8(r1)
        addi    r9,r1,STACK_FRAME_OVERHEAD
        CURRENT_THREAD_INFO(r10, r1)
        ld      r10,TI_FLAGS(r10)
        b       .Lsyscall_dotrace_cont

syscall_enosys:
        li      r3,-ENOSYS
        b       syscall_exit
        
syscall_exit_work:
#ifdef CONFIG_PPC_BOOK3S
        mtmsrd  r10,1           /* Restore RI */
#endif
        /* If TIF_RESTOREALL is set, don't scribble on either r3 or ccr.
         If TIF_NOERROR is set, just save r3 as it is. */

        andi.   r0,r9,_TIF_RESTOREALL
        beq+    0f
        REST_NVGPRS(r1)
        b       2f
0:      cmpld   r3,r11          /* r10 is -LAST_ERRNO */
        blt+    1f
        andi.   r0,r9,_TIF_NOERROR
        bne-    1f
        ld      r5,_CCR(r1)
        neg     r3,r3
        oris    r5,r5,0x1000    /* Set SO bit in CR */
        std     r5,_CCR(r1)
1:      std     r3,GPR3(r1)
2:      andi.   r0,r9,(_TIF_PERSYSCALL_MASK)
        beq     4f

        /* Clear per-syscall TIF flags if any are set.  */

        li      r11,_TIF_PERSYSCALL_MASK
        addi    r12,r12,TI_FLAGS
3:      ldarx   r10,0,r12
        andc    r10,r10,r11
        stdcx.  r10,0,r12
        bne-    3b
        subi    r12,r12,TI_FLAGS

4:      /* Anything else left to do? */
        SET_DEFAULT_THREAD_PPR(r3, r10)         /* Set thread.ppr = 3 */
        andi.   r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SINGLESTEP)
        beq     .ret_from_except_lite

        /* Re-enable interrupts */
#ifdef CONFIG_PPC_BOOK3E
        wrteei  1
#else
        ld      r10,PACAKMSR(r13)
        ori     r10,r10,MSR_EE
        mtmsrd  r10,1
#endif /* CONFIG_PPC_BOOK3E */

        bl      .save_nvgprs
        addi    r3,r1,STACK_FRAME_OVERHEAD
        bl      .do_syscall_trace_leave
        b       .ret_from_except

/* Save non-volatile GPRs, if not already saved. */
_GLOBAL(save_nvgprs)
        ld      r11,_TRAP(r1)
        andi.   r0,r11,1
        beqlr-
        SAVE_NVGPRS(r1)
        clrrdi  r0,r11,1
        std     r0,_TRAP(r1)
        blr

        
/*
 * The sigsuspend and rt_sigsuspend system calls can call do_signal
 * and thus put the process into the stopped state where we might
 * want to examine its user state with ptrace.  Therefore we need
 * to save all the nonvolatile registers (r14 - r31) before calling
 * the C code.  Similarly, fork, vfork and clone need the full
 * register state on the stack so that it can be copied to the child.
 */

_GLOBAL(ppc_fork)
        bl      .save_nvgprs
        bl      .sys_fork
        b       syscall_exit

_GLOBAL(ppc_vfork)
        bl      .save_nvgprs
        bl      .sys_vfork
        b       syscall_exit

_GLOBAL(ppc_clone)
        bl      .save_nvgprs
        bl      .sys_clone
        b       syscall_exit

_GLOBAL(ppc32_swapcontext)
        bl      .save_nvgprs
        bl      .compat_sys_swapcontext
        b       syscall_exit

_GLOBAL(ppc64_swapcontext)
        bl      .save_nvgprs
        bl      .sys_swapcontext
        b       syscall_exit

_GLOBAL(ret_from_fork)
        bl      .schedule_tail
        REST_NVGPRS(r1)
        li      r3,0
        b       syscall_exit

_GLOBAL(ret_from_kernel_thread)
        bl      .schedule_tail
        REST_NVGPRS(r1)
        ld      r14, 0(r14)
        mtlr    r14
        mr      r3,r15
        blrl
        li      r3,0
        b       syscall_exit

        .section        ".toc","aw"
DSCR_DEFAULT:
        .tc dscr_default[TC],dscr_default

        .section        ".text"

/*
 * This routine switches between two different tasks.  The process
 * state of one is saved on its kernel stack.  Then the state
 * of the other is restored from its kernel stack.  The memory
 * management hardware is updated to the second process's state.
 * Finally, we can return to the second process, via ret_from_except.
 * On entry, r3 points to the THREAD for the current task, r4
 * points to the THREAD for the new task.
 *
 * Note: there are two ways to get to the "going out" portion
 * of this code; either by coming in via the entry (_switch)
 * or via "fork" which must set up an environment equivalent
 * to the "_switch" path.  If you change this you'll have to change
 * the fork code also.
 *
 * The code which creates the new task context is in 'copy_thread'
 * in arch/powerpc/kernel/process.c 
 */
        .align  7
_GLOBAL(_switch)
        mflr    r0
        std     r0,16(r1)
        stdu    r1,-SWITCH_FRAME_SIZE(r1)
        /* r3-r13 are caller saved -- Cort */
        SAVE_8GPRS(14, r1)
        SAVE_10GPRS(22, r1)
        mflr    r20             /* Return to switch caller */
        mfmsr   r22
        li      r0, MSR_FP
#ifdef CONFIG_VSX
BEGIN_FTR_SECTION
        oris    r0,r0,MSR_VSX@h /* Disable VSX */
END_FTR_SECTION_IFSET(CPU_FTR_VSX)
#endif /* CONFIG_VSX */
#ifdef CONFIG_ALTIVEC
BEGIN_FTR_SECTION
        oris    r0,r0,MSR_VEC@h /* Disable altivec */
        mfspr   r24,SPRN_VRSAVE /* save vrsave register value */
        std     r24,THREAD_VRSAVE(r3)
END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
#endif /* CONFIG_ALTIVEC */
#ifdef CONFIG_PPC64
BEGIN_FTR_SECTION
        mfspr   r25,SPRN_DSCR
        std     r25,THREAD_DSCR(r3)
END_FTR_SECTION_IFSET(CPU_FTR_DSCR)
#endif
        and.    r0,r0,r22
        beq+    1f
        andc    r22,r22,r0
        MTMSRD(r22)
        isync
1:      std     r20,_NIP(r1)
        mfcr    r23
        std     r23,_CCR(r1)
        std     r1,KSP(r3)      /* Set old stack pointer */

#ifdef CONFIG_PPC_BOOK3S_64
BEGIN_FTR_SECTION
        /*
         * Back up the TAR across context switches.  Note that the TAR is not
         * available for use in the kernel.  (To provide this, the TAR should
         * be backed up/restored on exception entry/exit instead, and be in
         * pt_regs.  FIXME, this should be in pt_regs anyway (for debug).)
         */
        mfspr   r0,SPRN_TAR
        std     r0,THREAD_TAR(r3)

        /* Event based branch registers */
        mfspr   r0, SPRN_BESCR
        std     r0, THREAD_BESCR(r3)
        mfspr   r0, SPRN_EBBHR
        std     r0, THREAD_EBBHR(r3)
        mfspr   r0, SPRN_EBBRR
        std     r0, THREAD_EBBRR(r3)
END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
#endif

#ifdef CONFIG_SMP
        /* We need a sync somewhere here to make sure that if the
         * previous task gets rescheduled on another CPU, it sees all
         * stores it has performed on this one.
         */
        sync
#endif /* CONFIG_SMP */

        /*
         * If we optimise away the clear of the reservation in system
         * calls because we know the CPU tracks the address of the
         * reservation, then we need to clear it here to cover the
         * case that the kernel context switch path has no larx
         * instructions.
         */
BEGIN_FTR_SECTION
        ldarx   r6,0,r1
END_FTR_SECTION_IFSET(CPU_FTR_STCX_CHECKS_ADDRESS)

#ifdef CONFIG_PPC_BOOK3S
/* Cancel all explict user streams as they will have no use after context
 * switch and will stop the HW from creating streams itself
 */
        DCBT_STOP_ALL_STREAM_IDS(r6)
#endif

        addi    r6,r4,-THREAD   /* Convert THREAD to 'current' */
        std     r6,PACACURRENT(r13)     /* Set new 'current' */

        ld      r8,KSP(r4)      /* new stack pointer */
#ifdef CONFIG_PPC_BOOK3S
BEGIN_FTR_SECTION
  BEGIN_FTR_SECTION_NESTED(95)
        clrrdi  r6,r8,28        /* get its ESID */
        clrrdi  r9,r1,28        /* get current sp ESID */
  FTR_SECTION_ELSE_NESTED(95)
        clrrdi  r6,r8,40        /* get its 1T ESID */
        clrrdi  r9,r1,40        /* get current sp 1T ESID */
  ALT_MMU_FTR_SECTION_END_NESTED_IFCLR(MMU_FTR_1T_SEGMENT, 95)
FTR_SECTION_ELSE
        b       2f
ALT_MMU_FTR_SECTION_END_IFSET(MMU_FTR_SLB)
        clrldi. r0,r6,2         /* is new ESID c00000000? */
        cmpd    cr1,r6,r9       /* or is new ESID the same as current ESID? */
        cror    eq,4*cr1+eq,eq
        beq     2f              /* if yes, don't slbie it */

        /* Bolt in the new stack SLB entry */
        ld      r7,KSP_VSID(r4) /* Get new stack's VSID */
        oris    r0,r6,(SLB_ESID_V)@h
        ori     r0,r0,(SLB_NUM_BOLTED-1)@l
BEGIN_FTR_SECTION
        li      r9,MMU_SEGSIZE_1T       /* insert B field */
        oris    r6,r6,(MMU_SEGSIZE_1T << SLBIE_SSIZE_SHIFT)@h
        rldimi  r7,r9,SLB_VSID_SSIZE_SHIFT,0
END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)

        /* Update the last bolted SLB.  No write barriers are needed
         * here, provided we only update the current CPU's SLB shadow
         * buffer.
         */
        ld      r9,PACA_SLBSHADOWPTR(r13)
        li      r12,0
        std     r12,SLBSHADOW_STACKESID(r9) /* Clear ESID */
        std     r7,SLBSHADOW_STACKVSID(r9)  /* Save VSID */
        std     r0,SLBSHADOW_STACKESID(r9)  /* Save ESID */

        /* No need to check for MMU_FTR_NO_SLBIE_B here, since when
         * we have 1TB segments, the only CPUs known to have the errata
         * only support less than 1TB of system memory and we'll never
         * actually hit this code path.
         */

        slbie   r6
        slbie   r6              /* Workaround POWER5 < DD2.1 issue */
        slbmte  r7,r0
        isync
2:
#endif /* !CONFIG_PPC_BOOK3S */

        CURRENT_THREAD_INFO(r7, r8)  /* base of new stack */
        /* Note: this uses SWITCH_FRAME_SIZE rather than INT_FRAME_SIZE
           because we don't need to leave the 288-byte ABI gap at the
           top of the kernel stack. */
        addi    r7,r7,THREAD_SIZE-SWITCH_FRAME_SIZE

        mr      r1,r8           /* start using new stack pointer */
        std     r7,PACAKSAVE(r13)

#ifdef CONFIG_PPC_BOOK3S_64
BEGIN_FTR_SECTION
        /* Event based branch registers */
        ld      r0, THREAD_BESCR(r4)
        mtspr   SPRN_BESCR, r0
        ld      r0, THREAD_EBBHR(r4)
        mtspr   SPRN_EBBHR, r0
        ld      r0, THREAD_EBBRR(r4)
        mtspr   SPRN_EBBRR, r0

        ld      r0,THREAD_TAR(r4)
        mtspr   SPRN_TAR,r0
END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
#endif

#ifdef CONFIG_ALTIVEC
BEGIN_FTR_SECTION
        ld      r0,THREAD_VRSAVE(r4)
        mtspr   SPRN_VRSAVE,r0          /* if G4, restore VRSAVE reg */
END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
#endif /* CONFIG_ALTIVEC */
#ifdef CONFIG_PPC64
BEGIN_FTR_SECTION
        lwz     r6,THREAD_DSCR_INHERIT(r4)
        ld      r7,DSCR_DEFAULT@toc(2)
        ld      r0,THREAD_DSCR(r4)
        cmpwi   r6,0
        bne     1f
        ld      r0,0(r7)
1:      cmpd    r0,r25
        beq     2f
        mtspr   SPRN_DSCR,r0
2:
END_FTR_SECTION_IFSET(CPU_FTR_DSCR)
#endif

        ld      r6,_CCR(r1)
        mtcrf   0xFF,r6

        /* r3-r13 are destroyed -- Cort */
        REST_8GPRS(14, r1)
        REST_10GPRS(22, r1)

        /* convert old thread to its task_struct for return value */
        addi    r3,r3,-THREAD
        ld      r7,_NIP(r1)     /* Return to _switch caller in new task */
        mtlr    r7
        addi    r1,r1,SWITCH_FRAME_SIZE
        blr

        .align  7
_GLOBAL(ret_from_except)
        ld      r11,_TRAP(r1)
        andi.   r0,r11,1
        bne     .ret_from_except_lite
        REST_NVGPRS(r1)

_GLOBAL(ret_from_except_lite)
        /*
         * Disable interrupts so that current_thread_info()->flags
         * can't change between when we test it and when we return
         * from the interrupt.
         */
#ifdef CONFIG_PPC_BOOK3E
        wrteei  0
#else
        ld      r10,PACAKMSR(r13) /* Get kernel MSR without EE */
        mtmsrd  r10,1             /* Update machine state */
#endif /* CONFIG_PPC_BOOK3E */

        CURRENT_THREAD_INFO(r9, r1)
        ld      r3,_MSR(r1)
#ifdef CONFIG_PPC_BOOK3E
        ld      r10,PACACURRENT(r13)
#endif /* CONFIG_PPC_BOOK3E */
        ld      r4,TI_FLAGS(r9)
        andi.   r3,r3,MSR_PR
        beq     resume_kernel
#ifdef CONFIG_PPC_BOOK3E
        lwz     r3,(THREAD+THREAD_DBCR0)(r10)
#endif /* CONFIG_PPC_BOOK3E */

        /* Check current_thread_info()->flags */
        andi.   r0,r4,_TIF_USER_WORK_MASK
#ifdef CONFIG_PPC_BOOK3E
        bne     1f
        /*
         * Check to see if the dbcr0 register is set up to debug.
         * Use the internal debug mode bit to do this.
         */
        andis.  r0,r3,DBCR0_IDM@h
        beq     restore
        mfmsr   r0
        rlwinm  r0,r0,0,~MSR_DE /* Clear MSR.DE */
        mtmsr   r0
        mtspr   SPRN_DBCR0,r3
        li      r10, -1
        mtspr   SPRN_DBSR,r10
        b       restore
#else
        beq     restore
#endif
1:      andi.   r0,r4,_TIF_NEED_RESCHED
        beq     2f
        bl      .restore_interrupts
        SCHEDULE_USER
        b       .ret_from_except_lite

2:      bl      .save_nvgprs
        bl      .restore_interrupts
        addi    r3,r1,STACK_FRAME_OVERHEAD
        bl      .do_notify_resume
        b       .ret_from_except

resume_kernel:
        /* check current_thread_info, _TIF_EMULATE_STACK_STORE */
        CURRENT_THREAD_INFO(r9, r1)
        ld      r8,TI_FLAGS(r9)
        andis.  r8,r8,_TIF_EMULATE_STACK_STORE@h
        beq+    1f

        addi    r8,r1,INT_FRAME_SIZE    /* Get the kprobed function entry */

        lwz     r3,GPR1(r1)
        subi    r3,r3,INT_FRAME_SIZE    /* dst: Allocate a trampoline exception frame */
        mr      r4,r1                   /* src:  current exception frame */
        mr      r1,r3                   /* Reroute the trampoline frame to r1 */

        /* Copy from the original to the trampoline. */
        li      r5,INT_FRAME_SIZE/8     /* size: INT_FRAME_SIZE */
        li      r6,0                    /* start offset: 0 */
        mtctr   r5
2:      ldx     r0,r6,r4
        stdx    r0,r6,r3
        addi    r6,r6,8
        bdnz    2b

        /* Do real store operation to complete stwu */
        lwz     r5,GPR1(r1)
        std     r8,0(r5)

        /* Clear _TIF_EMULATE_STACK_STORE flag */
        lis     r11,_TIF_EMULATE_STACK_STORE@h
        addi    r5,r9,TI_FLAGS
0:      ldarx   r4,0,r5
        andc    r4,r4,r11
        stdcx.  r4,0,r5
        bne-    0b
1:

#ifdef CONFIG_PREEMPT
        /* Check if we need to preempt */
        andi.   r0,r4,_TIF_NEED_RESCHED
        beq+    restore
        /* Check that preempt_count() == 0 and interrupts are enabled */
        lwz     r8,TI_PREEMPT(r9)
        cmpwi   cr1,r8,0
        ld      r0,SOFTE(r1)
        cmpdi   r0,0
        crandc  eq,cr1*4+eq,eq
        bne     restore

        /*
         * Here we are preempting the current task. We want to make
         * sure we are soft-disabled first
         */
        SOFT_DISABLE_INTS(r3,r4)
1:      bl      .preempt_schedule_irq

        /* Re-test flags and eventually loop */
        CURRENT_THREAD_INFO(r9, r1)
        ld      r4,TI_FLAGS(r9)
        andi.   r0,r4,_TIF_NEED_RESCHED
        bne     1b

        /*
         * arch_local_irq_restore() from preempt_schedule_irq above may
         * enable hard interrupt but we really should disable interrupts
         * when we return from the interrupt, and so that we don't get
         * interrupted after loading SRR0/1.
         */
#ifdef CONFIG_PPC_BOOK3E
        wrteei  0
#else
        ld      r10,PACAKMSR(r13) /* Get kernel MSR without EE */
        mtmsrd  r10,1             /* Update machine state */
#endif /* CONFIG_PPC_BOOK3E */
#endif /* CONFIG_PREEMPT */

        .globl  fast_exc_return_irq
fast_exc_return_irq:
restore:
        /*
         * This is the main kernel exit path. First we check if we
         * are about to re-enable interrupts
         */
        ld      r5,SOFTE(r1)
        lbz     r6,PACASOFTIRQEN(r13)
        cmpwi   cr0,r5,0
        beq     restore_irq_off

        /* We are enabling, were we already enabled ? Yes, just return */
        cmpwi   cr0,r6,1
        beq     cr0,do_restore

        /*
         * We are about to soft-enable interrupts (we are hard disabled
         * at this point). We check if there's anything that needs to
         * be replayed first.
         */
        lbz     r0,PACAIRQHAPPENED(r13)
        cmpwi   cr0,r0,0
        bne-    restore_check_irq_replay

        /*
         * Get here when nothing happened while soft-disabled, just
         * soft-enable and move-on. We will hard-enable as a side
         * effect of rfi
         */
restore_no_replay:
        TRACE_ENABLE_INTS
        li      r0,1
        stb     r0,PACASOFTIRQEN(r13);

        /*
         * Final return path. BookE is handled in a different file
         */
do_restore:
#ifdef CONFIG_PPC_BOOK3E
        b       .exception_return_book3e
#else
        /*
         * Clear the reservation. If we know the CPU tracks the address of
         * the reservation then we can potentially save some cycles and use
         * a larx. On POWER6 and POWER7 this is significantly faster.
         */
BEGIN_FTR_SECTION
        stdcx.  r0,0,r1         /* to clear the reservation */
FTR_SECTION_ELSE
        ldarx   r4,0,r1
ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)

        /*
         * Some code path such as load_up_fpu or altivec return directly
         * here. They run entirely hard disabled and do not alter the
         * interrupt state. They also don't use lwarx/stwcx. and thus
         * are known not to leave dangling reservations.
         */
        .globl  fast_exception_return
fast_exception_return:
        ld      r3,_MSR(r1)
        ld      r4,_CTR(r1)
        ld      r0,_LINK(r1)
        mtctr   r4
        mtlr    r0
        ld      r4,_XER(r1)
        mtspr   SPRN_XER,r4

        REST_8GPRS(5, r1)

        andi.   r0,r3,MSR_RI
        beq-    unrecov_restore

        /*
         * Clear RI before restoring r13.  If we are returning to
         * userspace and we take an exception after restoring r13,
         * we end up corrupting the userspace r13 value.
         */
        ld      r4,PACAKMSR(r13) /* Get kernel MSR without EE */
        andc    r4,r4,r0         /* r0 contains MSR_RI here */
        mtmsrd  r4,1

#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
        /* TM debug */
        std     r3, PACATMSCRATCH(r13) /* Stash returned-to MSR */
#endif
        /*
         * r13 is our per cpu area, only restore it if we are returning to
         * userspace the value stored in the stack frame may belong to
         * another CPU.
         */
        andi.   r0,r3,MSR_PR
        beq     1f
        ACCOUNT_CPU_USER_EXIT(r2, r4)
        RESTORE_PPR(r2, r4)
        REST_GPR(13, r1)
1:
        mtspr   SPRN_SRR1,r3

        ld      r2,_CCR(r1)
        mtcrf   0xFF,r2
        ld      r2,_NIP(r1)
        mtspr   SPRN_SRR0,r2

        ld      r0,GPR0(r1)
        ld      r2,GPR2(r1)
        ld      r3,GPR3(r1)
        ld      r4,GPR4(r1)
        ld      r1,GPR1(r1)

        rfid
        b       .       /* prevent speculative execution */

#endif /* CONFIG_PPC_BOOK3E */

        /*
         * We are returning to a context with interrupts soft disabled.
         *
         * However, we may also about to hard enable, so we need to
         * make sure that in this case, we also clear PACA_IRQ_HARD_DIS
         * or that bit can get out of sync and bad things will happen
         */
restore_irq_off:
        ld      r3,_MSR(r1)
        lbz     r7,PACAIRQHAPPENED(r13)
        andi.   r0,r3,MSR_EE
        beq     1f
        rlwinm  r7,r7,0,~PACA_IRQ_HARD_DIS
        stb     r7,PACAIRQHAPPENED(r13)
1:      li      r0,0
        stb     r0,PACASOFTIRQEN(r13);
        TRACE_DISABLE_INTS
        b       do_restore

        /*
         * Something did happen, check if a re-emit is needed
         * (this also clears paca->irq_happened)
         */
restore_check_irq_replay:
        /* XXX: We could implement a fast path here where we check
         * for irq_happened being just 0x01, in which case we can
         * clear it and return. That means that we would potentially
         * miss a decrementer having wrapped all the way around.
         *
         * Still, this might be useful for things like hash_page
         */
        bl      .__check_irq_replay
        cmpwi   cr0,r3,0
        beq     restore_no_replay
 
        /*
         * We need to re-emit an interrupt. We do so by re-using our
         * existing exception frame. We first change the trap value,
         * but we need to ensure we preserve the low nibble of it
         */
        ld      r4,_TRAP(r1)
        clrldi  r4,r4,60
        or      r4,r4,r3
        std     r4,_TRAP(r1)

        /*
         * Then find the right handler and call it. Interrupts are
         * still soft-disabled and we keep them that way.
        */
        cmpwi   cr0,r3,0x500
        bne     1f
        addi    r3,r1,STACK_FRAME_OVERHEAD;
        bl      .do_IRQ
        b       .ret_from_except
1:      cmpwi   cr0,r3,0x900
        bne     1f
        addi    r3,r1,STACK_FRAME_OVERHEAD;
        bl      .timer_interrupt
        b       .ret_from_except
#ifdef CONFIG_PPC_DOORBELL
1:
#ifdef CONFIG_PPC_BOOK3E
        cmpwi   cr0,r3,0x280
#else
        BEGIN_FTR_SECTION
                cmpwi   cr0,r3,0xe80
        FTR_SECTION_ELSE
                cmpwi   cr0,r3,0xa00
        ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE)
#endif /* CONFIG_PPC_BOOK3E */
        bne     1f
        addi    r3,r1,STACK_FRAME_OVERHEAD;
        bl      .doorbell_exception
        b       .ret_from_except
#endif /* CONFIG_PPC_DOORBELL */
1:      b       .ret_from_except /* What else to do here ? */
 
unrecov_restore:
        addi    r3,r1,STACK_FRAME_OVERHEAD
        bl      .unrecoverable_exception
        b       unrecov_restore

#ifdef CONFIG_PPC_RTAS
/*
 * On CHRP, the Run-Time Abstraction Services (RTAS) have to be
 * called with the MMU off.
 *
 * In addition, we need to be in 32b mode, at least for now.
 * 
 * Note: r3 is an input parameter to rtas, so don't trash it...
 */
_GLOBAL(enter_rtas)
        mflr    r0
        std     r0,16(r1)
        stdu    r1,-RTAS_FRAME_SIZE(r1) /* Save SP and create stack space. */

        /* Because RTAS is running in 32b mode, it clobbers the high order half
         * of all registers that it saves.  We therefore save those registers
         * RTAS might touch to the stack.  (r0, r3-r13 are caller saved)
         */
        SAVE_GPR(2, r1)                 /* Save the TOC */
        SAVE_GPR(13, r1)                /* Save paca */
        SAVE_8GPRS(14, r1)              /* Save the non-volatiles */
        SAVE_10GPRS(22, r1)             /* ditto */

        mfcr    r4
        std     r4,_CCR(r1)
        mfctr   r5
        std     r5,_CTR(r1)
        mfspr   r6,SPRN_XER
        std     r6,_XER(r1)
        mfdar   r7
        std     r7,_DAR(r1)
        mfdsisr r8
        std     r8,_DSISR(r1)

        /* Temporary workaround to clear CR until RTAS can be modified to
         * ignore all bits.
         */
        li      r0,0
        mtcr    r0

#ifdef CONFIG_BUG       
        /* There is no way it is acceptable to get here with interrupts enabled,
         * check it with the asm equivalent of WARN_ON
         */
        lbz     r0,PACASOFTIRQEN(r13)
1:      tdnei   r0,0
        EMIT_BUG_ENTRY 1b,__FILE__,__LINE__,BUGFLAG_WARNING
#endif
        
        /* Hard-disable interrupts */
        mfmsr   r6
        rldicl  r7,r6,48,1
        rotldi  r7,r7,16
        mtmsrd  r7,1

        /* Unfortunately, the stack pointer and the MSR are also clobbered,
         * so they are saved in the PACA which allows us to restore
         * our original state after RTAS returns.
         */
        std     r1,PACAR1(r13)
        std     r6,PACASAVEDMSR(r13)

        /* Setup our real return addr */        
        LOAD_REG_ADDR(r4,.rtas_return_loc)
        clrldi  r4,r4,2                 /* convert to realmode address */
        mtlr    r4

        li      r0,0
        ori     r0,r0,MSR_EE|MSR_SE|MSR_BE|MSR_RI
        andc    r0,r6,r0
        
        li      r9,1
        rldicr  r9,r9,MSR_SF_LG,(63-MSR_SF_LG)
        ori     r9,r9,MSR_IR|MSR_DR|MSR_FE0|MSR_FE1|MSR_FP|MSR_RI
        andc    r6,r0,r9
        sync                            /* disable interrupts so SRR0/1 */
        mtmsrd  r0                      /* don't get trashed */

        LOAD_REG_ADDR(r4, rtas)
        ld      r5,RTASENTRY(r4)        /* get the rtas->entry value */
        ld      r4,RTASBASE(r4)         /* get the rtas->base value */
        
        mtspr   SPRN_SRR0,r5
        mtspr   SPRN_SRR1,r6
        rfid
        b       .       /* prevent speculative execution */

_STATIC(rtas_return_loc)
        /* relocation is off at this point */
        GET_PACA(r4)
        clrldi  r4,r4,2                 /* convert to realmode address */

        bcl     20,31,$+4
0:      mflr    r3
        ld      r3,(1f-0b)(r3)          /* get &.rtas_restore_regs */

        mfmsr   r6
        li      r0,MSR_RI
        andc    r6,r6,r0
        sync    
        mtmsrd  r6
        
        ld      r1,PACAR1(r4)           /* Restore our SP */
        ld      r4,PACASAVEDMSR(r4)     /* Restore our MSR */

        mtspr   SPRN_SRR0,r3
        mtspr   SPRN_SRR1,r4
        rfid
        b       .       /* prevent speculative execution */

        .align  3
1:      .llong  .rtas_restore_regs

_STATIC(rtas_restore_regs)
        /* relocation is on at this point */
        REST_GPR(2, r1)                 /* Restore the TOC */
        REST_GPR(13, r1)                /* Restore paca */
        REST_8GPRS(14, r1)              /* Restore the non-volatiles */
        REST_10GPRS(22, r1)             /* ditto */

        GET_PACA(r13)

        ld      r4,_CCR(r1)
        mtcr    r4
        ld      r5,_CTR(r1)
        mtctr   r5
        ld      r6,_XER(r1)
        mtspr   SPRN_XER,r6
        ld      r7,_DAR(r1)
        mtdar   r7
        ld      r8,_DSISR(r1)
        mtdsisr r8

        addi    r1,r1,RTAS_FRAME_SIZE   /* Unstack our frame */
        ld      r0,16(r1)               /* get return address */

        mtlr    r0
        blr                             /* return to caller */

#endif /* CONFIG_PPC_RTAS */

_GLOBAL(enter_prom)
        mflr    r0
        std     r0,16(r1)
        stdu    r1,-PROM_FRAME_SIZE(r1) /* Save SP and create stack space */

        /* Because PROM is running in 32b mode, it clobbers the high order half
         * of all registers that it saves.  We therefore save those registers
         * PROM might touch to the stack.  (r0, r3-r13 are caller saved)
         */
        SAVE_GPR(2, r1)
        SAVE_GPR(13, r1)
        SAVE_8GPRS(14, r1)
        SAVE_10GPRS(22, r1)
        mfcr    r10
        mfmsr   r11
        std     r10,_CCR(r1)
        std     r11,_MSR(r1)

        /* Get the PROM entrypoint */
        mtlr    r4

        /* Switch MSR to 32 bits mode
         */
#ifdef CONFIG_PPC_BOOK3E
        rlwinm  r11,r11,0,1,31
        mtmsr   r11
#else /* CONFIG_PPC_BOOK3E */
        mfmsr   r11
        li      r12,1
        rldicr  r12,r12,MSR_SF_LG,(63-MSR_SF_LG)
        andc    r11,r11,r12
        li      r12,1
        rldicr  r12,r12,MSR_ISF_LG,(63-MSR_ISF_LG)
        andc    r11,r11,r12
        mtmsrd  r11
#endif /* CONFIG_PPC_BOOK3E */
        isync

        /* Enter PROM here... */
        blrl

        /* Just make sure that r1 top 32 bits didn't get
         * corrupt by OF
         */
        rldicl  r1,r1,0,32

        /* Restore the MSR (back to 64 bits) */
        ld      r0,_MSR(r1)
        MTMSRD(r0)
        isync

        /* Restore other registers */
        REST_GPR(2, r1)
        REST_GPR(13, r1)
        REST_8GPRS(14, r1)
        REST_10GPRS(22, r1)
        ld      r4,_CCR(r1)
        mtcr    r4
        
        addi    r1,r1,PROM_FRAME_SIZE
        ld      r0,16(r1)
        mtlr    r0
        blr

#ifdef CONFIG_FUNCTION_TRACER
#ifdef CONFIG_DYNAMIC_FTRACE
_GLOBAL(mcount)
_GLOBAL(_mcount)
        blr

_GLOBAL(ftrace_caller)
        /* Taken from output of objdump from lib64/glibc */
        mflr    r3
        ld      r11, 0(r1)
        stdu    r1, -112(r1)
        std     r3, 128(r1)
        ld      r4, 16(r11)
        subi    r3, r3, MCOUNT_INSN_SIZE
.globl ftrace_call
ftrace_call:
        bl      ftrace_stub
        nop
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
.globl ftrace_graph_call
ftrace_graph_call:
        b       ftrace_graph_stub
_GLOBAL(ftrace_graph_stub)
#endif
        ld      r0, 128(r1)
        mtlr    r0
        addi    r1, r1, 112
_GLOBAL(ftrace_stub)
        blr
#else
_GLOBAL(mcount)
        blr

_GLOBAL(_mcount)
        /* Taken from output of objdump from lib64/glibc */
        mflr    r3
        ld      r11, 0(r1)
        stdu    r1, -112(r1)
        std     r3, 128(r1)
        ld      r4, 16(r11)

        subi    r3, r3, MCOUNT_INSN_SIZE
        LOAD_REG_ADDR(r5,ftrace_trace_function)
        ld      r5,0(r5)
        ld      r5,0(r5)
        mtctr   r5
        bctrl
        nop


#ifdef CONFIG_FUNCTION_GRAPH_TRACER
        b       ftrace_graph_caller
#endif
        ld      r0, 128(r1)
        mtlr    r0
        addi    r1, r1, 112
_GLOBAL(ftrace_stub)
        blr

#endif /* CONFIG_DYNAMIC_FTRACE */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
_GLOBAL(ftrace_graph_caller)
        /* load r4 with local address */
        ld      r4, 128(r1)
        subi    r4, r4, MCOUNT_INSN_SIZE

        /* get the parent address */
        ld      r11, 112(r1)
        addi    r3, r11, 16

        bl      .prepare_ftrace_return
        nop

        ld      r0, 128(r1)
        mtlr    r0
        addi    r1, r1, 112
        blr

_GLOBAL(return_to_handler)
        /* need to save return values */
        std     r4,  -24(r1)
        std     r3,  -16(r1)
        std     r31, -8(r1)
        mr      r31, r1
        stdu    r1, -112(r1)

        bl      .ftrace_return_to_handler
        nop

        /* return value has real return address */
        mtlr    r3

        ld      r1, 0(r1)
        ld      r4,  -24(r1)
        ld      r3,  -16(r1)
        ld      r31, -8(r1)

        /* Jump back to real return address */
        blr

_GLOBAL(mod_return_to_handler)
        /* need to save return values */
        std     r4,  -32(r1)
        std     r3,  -24(r1)
        /* save TOC */
        std     r2,  -16(r1)
        std     r31, -8(r1)
        mr      r31, r1
        stdu    r1, -112(r1)

        /*
         * We are in a module using the module's TOC.
         * Switch to our TOC to run inside the core kernel.
         */
        ld      r2, PACATOC(r13)

        bl      .ftrace_return_to_handler
        nop

        /* return value has real return address */
        mtlr    r3

        ld      r1, 0(r1)
        ld      r4,  -32(r1)
        ld      r3,  -24(r1)
        ld      r2,  -16(r1)
        ld      r31, -8(r1)

        /* Jump back to real return address */
        blr
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
#endif /* CONFIG_FUNCTION_TRACER */